1. Field of the Invention
The present invention relates to a method for the manufacture of an electromechanical sensor element and to a sensor element.
2. Discussion of the Related Art
Previously known is a so-called electret field, i.e. a permanent electric charge injected into a dielectric material by ionizing. A film applicable for use as a sensor film in the sensor element of the invention is presented in U.S. Pat. No. 4,654,546, in which a dielectric plastic film, such as polypropylene, containing flat or torn gas bubbles or voids is used to form a so-called cellular electret film. Both surfaces of the film are metal-coated. WO specification 96/06718 presents a method for swelling a foamed plastic film, whereby the amount of gas contained in the film can be more than doubled. Patent specification FI 913741 presents various electric structures for sensor elements. Previously known are also fibrous polarized electret films, as presented e.g. in U.S. Pat. No. 4,874,659. Other known elements applicable in the sensor element of the invention are piezoelectric sensor films, such as PVDF.